The present disclosure relates to methods, systems and apparatuses for building heating, ventilation, and air conditioning (“HVAC”) systems and, more particularly to assembly, verification, and maintenance of a fully functional terminal unit, or a functionally equivalent device called a lab valve damper when installed in certain environments.
In general, HVAC systems control the temperature and humidity of indoor air. In most HVAC systems, air is drawn in, filtered, cooled and dehumidified or heated and humidified, and then delivered to an air conditioned space. The greatest portion of incoming air is drawn from the air conditioned space for recirculation through the HVAC system. HVAC system includes fans and ductwork for moving conditioned air to where it is needed while passing it through cooling and/or a heating sections of the ductwork.
One risk which should be addressed in designing and operating HVAC systems is that of biological contamination by bacteria, molds, and viruses. In recent years, biological problems in indoor environments have received considerable attention. Most frequently, molds, bacteria and/or virus grow wherever water collects in a HVAC systems ductwork, such as at its cooling sections.
Poor indoor air quality (“IAQ”) and the spread of infectious disease through a HVAC system, at a minimum, can reduce worker productivity and increase absenteeism. Even more alarming is the potential liability for illnesses suffered by workers due to poor IAQ. The Legionnaires' disease outbreak in Philadelphia in 1976, is probably the most publicized instance of illness caused by poor IAQ. Even if contamination by molds and bacteria doesn't affect workers, their growth within HVAC system equipment creates maintenance problems which are very costly to correct. Left uncorrected, these problems exacerbate and, at a minimum, eventually reduce system's heat transfer efficiency.
HVAC systems in residential, commercial, education and research buildings usually include metallic pipes, hollow composite materials such as tubes, and the like. The systems are typically supported from and between floor or ceiling joists. The HVAC system typically includes a primary or main duct. A series of smaller branch ducts which extend from the main duct are mounted between adjacent floor or ceiling joists. Such main and branch ducts are normally supported by metal hangers located between the joists. Often the branch ducts include pipes and conduit lines for transporting liquid or gas which are suspended from ceiling joists or an adjacent wall typically with Unistrut®, threaded rod, couplings, and various hanger brackets.
Piping and conduits that supply gas and/or liquids within buildings benefit from careful preparation. Builders or contractors typically use ladders or scaffolding to reach areas where piping is routed so installation may be cumbersome. Occasionally the pipe or conduits are prepared on the ground and installed by ladder as more complete assemblies. Pipe and conduit assemblies prepared on the ground or a floor of a building under construction are more unwieldy than the unassembled components, but pre-assembly is often more practical. Furthermore, conditions existing at construction sites and the number of differing types of components used in assembling a HVAC system render cataloging known HVAC components a challenge.
Generically, a terminal unit, also sometimes referred to as an air handling unit, is a HVAC system component that is located near an air conditioned space that regulates the temperature and/or volume of air supplied to the space. When providing air to a more critical environment such as a laboratory, an almost identical ductwork section is frequently referred to as a lab valve damper rather than as a terminal unit, with the distinction generally relating to the precision with which the unit controls the temperature and humidity of conditioned air. As used throughout this document, the phrase terminal unit encompasses either a terminal unit or a lab valve damper.
A HVAC system may be assembled using any one of several different types of terminal units. Generally, the mechanical portion of a terminal unit includes a casing through which air flows during operation of a HVAC system. Accordingly, the casing includes an inlet for receiving air from ductwork of a HVAC system, and an outlet for supplying air to a space in a building. Casings are usually fabricated from 22 gauge galvanized sheet steel.
Due to the use of such light material, casings are easily damaged during shipping to a building site and during installation into the HVAC system. Those familiar with such damage to terminal unit casings frequently refer to it as “oil canning” because it resembles how a light gauge oil can collapses as the liquid flows out.
In a typical hydronic (all-water) HVAC system, the mechanical portion of a terminal unit includes a heat exchanging coil. Heated and/or cooled water is pumped from a central plant through pipes to the coil. Air from the HVAC system's ductwork passes through the coil after entering and before leaving the casing. Usually, a single terminal unit is dedicated for heating and/or cooling each air conditioned space. Air from the duct connected to the terminal unit passes through the coil to be heated and/or cooled by water flowing through the coil before the air enters the air conditioned space.
A Variable Air Volume (“VAV”) HVAC system, in response to a control signal from a thermostat or room sensor, supplies only that volume of hot and/or cold air to an air conditioned space needed to satisfy the space's thermal load. A VAV HVAC system meets changing cooling and/or heating requirements by adjusting the amount, rather than the temperature, of air that flows to a space. For most buildings, a VAV HVAC system yields the best combination of comfort, first cost, and life cycle cost.
A VAV terminal unit is a relatively complex assembly which includes sheet metal, plumbing, electrical and pneumatic components. For example, a VAV terminal unit includes an airflow sensor that senses the velocity of air entering the terminal unit. To adjust the volume of cold air, a VAV terminal unit frequently includes a damper which automatically opens and closes as needed.
As a space's thermal load decreases, the damper starts closing thereby reducing the amount of heated or cooled air supplied to the space. Alternatively, the volume of air entering a space may be controlled by varying the speed of a fan included in the terminal unit. For either type of VAV terminal unit, VAV HVAC systems save energy consumed by fans in comparison with alternative HVAC systems by continually adjusting airflow to the heating and/or cooling required.
To be operable and fully-functional, terminal units for a hydronic HVAC system often include a coil, ductwork for supplying air to the coil and receiving air from the coil, plumbing for supplying water into and receiving water from the coil, and a control valve for regulating the amount of water flowing through the coil.
To match the flow of air through the terminal unit's ductwork to the profile of the coil, the terminal unit's ductwork may include transition sections both for air entering the coil and for air leaving the coil. In addition, a terminal unit may also include a re-heat coil, and/or a sound attenuator. In a terminal unit adapted for use in a VAV HVAC system, the terminal unit's ductwork may also include a damper and a damper actuator or variable speed fan for controlling the volume of air supplied by the terminal unit, and an airflow sensor for sensing the volume of air passing through the terminal unit.
Usually, all of the various parts needed to assemble a fully-functional VAV HVAC system's terminal unit arrive at building construction sites as separate components.
Generally, these components are then assembled into a fully functional terminal unit at the construction site. Due to cluttered working conditions usually existing at a construction site where workers skilled in different crafts, e.g. plumbing, electrical, structural, etc., must concurrently collaborate to complete the building project, assembling the various components into a fully functional terminal unit may occupy the better part of a day. Furthermore, present practices and equipment are poorly adapted for swiftly constructing a high quality HVAC system that is easily commissioned.
For example, because it is less expensive to wire a HVAC system's terminal units with 24 volt low voltage electrical power rather than 220 or 110 volt power, presently sections of buildings include transformer trees which an electrician generally assembles by installing multiple step down transformers on an electrical panel. This technique permits wiring 220 or 110 volt electrical power to the transformer tree on each panel, with the 24 volt low voltage electrical power then being wired individually from a transformer on the panel over distances of five (5) to one hundred (100) feet to a terminal units for energizing its Direct Digital Control (“DDC”) controller, and 2 way or 3 way automatic temperature control (“ATC”) control valve.
Usually, terminal units are supported from a building using angle brackets, straps, or thread rod. Usually these support devices are attached directly to the terminal unit. Terminal unit casings are usually made using 22 gauge sheet metal. Due to the use of this light material, casings are easily dented or bent during installation.
With current construction site labor costing up to $80.00/hour or more, assembling a terminal unit at a construction site may cost $500.00 to $1,000.00 for labor alone. Furthermore, terminal units assembled at a construction site generally differ from one another due to assembly by different craftsmen, and insufficient use of identical components in assembling each terminal unit. Due to conditions existing at construction sites and the number of differing types of components used in assembling a HVAC system, cataloging the components used in assembling the system is impractical. Lastly, construction sites generally lack any facilities for individually pre-testing building components, such as terminal units, assembled on-site.
After assembling a HVAC system, it should be activated, tested and commissioned to ensure IAQ. Testing a HVAC system only after it is completely assembled inevitably results in many hours of problem-solving and leak-hunting. Usually, there are leaky joints, broken valves, damaged pipes, leaky coils and improperly assembled components that must be tracked down which further increases building costs. After finding a faulty component, it must be identified, ordered and replaced which takes time and delays completion of the building project. Furthermore, years after a building project is complete to maintain IAQ a building manager responsible for the HVAC system's maintenance will often have to identify and replace broken components.
The preceding considerations arising from construction site assembly of fully functional terminal units slows construction, increase building costs, requires rework when a terminal unit experiences an initial failure, and ultimately makes more difficult and expensive maintaining a building's HVAC system years after those responsible for its assembly are no longer available.